Yahoo is the latest company to reveal its dealings with the US authorities, following revelations about the Prism surveillance programme.

It said it had received between 12,000 and 13,000 US government requests for user data in the past year and a half.

Most of them had "concerned fraud, homicides, kidnappings, and other criminal investigations", it said.

Yahoo voiced frustration that it was unable to reveal the number of requests that had concerned national security.

It urged the government to "reconsider its stance on this issue".

"Like all companies, Yahoo cannot lawfully break out Fisa [Foreign Intelligence Surveillance Act] request numbers at this time because those numbers are classified," it said in a blog post by chief executive Marissa Mayer and general counsel Ron Bell.

Under pressure

FISA is widely seen as the legislation under which Prism operated.

Earlier in the week Twitter also said it was important to be able to publish numbers of national security requests.

And Google said lumping police requests with national security requests was "a step back for users".

Tech firms have been under pressure to disclose information about data passed to the National Security Agency (NSA) since the Guardian and Washington Post revealed the existence of Prism - a programme giving the NSA access to user data held on the servers of tech firms including Microsoft, Yahoo, Google, Facebook, PalTalk, AOL, and Apple.

The NSA later confirmed the existence of the surveillance scheme as well as a separate phone-records programme, which it said had helped it thwart terrorist plots in the US and more than 20 other countries.

Rebuilding trust

Technology companies, which initially denied any knowledge of the Prism project, are now rushing to rebuild trust from users shocked at the idea that their data was viewable by the authorities.

Yahoo laid out plans to publish a twice-yearly global transparency report, the first of which will be issued "later this summer".

"Democracy demands accountability," the blog said.

"We appreciate - and do not take for granted- the trust you place in us."

Other companies have been quick to rebut suggestions they simply hand over data whenever asked.

"Only if appropriate, we retrieve and deliver the narrowest possible set of information to the authorities," said Apple.

Facebook's general counsel Ted Ullyot said: "We aggressively protect our users' data when confronted with such requests; we frequently reject such requests outright, or require the government to substantially scale down its requests, or simply give the government much less data than it has requested."

So far disclosures have revealed:

Apple received between 4,000 and 5,000 requests from federal, state and local authorities between December 2012 and May 2013

Facebook received between 9,000 and 10,000 requests between July and December 2012

Microsoft received between 6,000 and 7,000 requests between July and December 2012